Matthew 18:19

Again, I say unto you
As the words in the former verse seem to regard the whole body of the disciples, whose decisions in cases brought before them, declaring them just or unjust, are determinate and unalterable; these seem to respect the one or two, that should join the offended person in the reproof of the offender, and are spoken for their encouragement; who might think proper either to premise, or follow their engaging in such a work with prayer:

that if two of you shall agree on earth, as touching anything that
they shall ask;
both in the case before mentioned, and in any other thing: whether it be for themselves or others; to assist them in the ministry of the word, and give success to it, for the conversion of sinners; and in the performance of any miracle, for the confirmation of the Gospel; in the administration of ordinances, for the comfort of saints; and in laying on of censures, for the reclaiming of backsliders; or be it what it will that may be done, consistent with the glory of God, the purposes of his mind, and the declarations of his will, and the good of men, provided they agree in their requests; though they are here on earth, and at such a distance from heaven, from whence their help and assistance come:

it shall be done for them of my Father which is in heaven;
with whom nothing is impossible; and who, as he regards the effectual fervent prayer of any righteous man, so more, of two agreed together in anyone thing; and still more, of a church and community of saints in their united requests: a great encouragement this to social prayer, though ever so few are engaged in it.